Problem: Simplify the following expression: $p = \dfrac{a}{9} + \dfrac{6a}{7}$
Answer: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $9$ and $7$ $\lcm(9, 7) = 63$ $ p = \dfrac{7}{7} \cdot \dfrac{a}{9} + \dfrac{9}{9} \cdot \dfrac{6a}{7} $ $p = \dfrac{7a}{63} + \dfrac{54a}{63}$ $p = \dfrac{7a +54a}{63}$ $p = \dfrac{61a}{63}$